C++ Academy · Lesson

Durations and Clocks

Measure time intervals.

Lesson 1 of 413 steps

Durations and Clocks is a free C++ Academy lesson on CoddyKit. This is lesson 1 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, and your progress syncs across the web and the CoddyKit app. The C++ Academy course includes 4 lessons in total.

Why <chrono>?

The <chrono> library gives C++ a type-safe way to work with time. Instead of raw integers, you use strongly typed durations and time points so the compiler catches unit mistakes.

No more mixing up seconds and milliseconds.
Units are part of the type system.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    seconds s{5};
    std::cout << "Duration: " << s.count() << " seconds\n";
    return 0;
}

What Is a Duration?

A std::chrono::duration represents a span of time. It stores a count of ticks plus a ratio describing the tick period. Predefined aliases cover common units.

hours, minutes, seconds
milliseconds, microseconds, nanoseconds

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    milliseconds ms{1500};
    std::cout << ms.count() << " ms\n";
    return 0;
}

Duration Literals

The std::chrono_literals namespace lets you write durations with suffixes like 5s or 200ms, making code read like plain English.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono_literals;
    auto wait = 3s;
    auto blink = 250ms;
    std::cout << wait.count() << "s, " << blink.count() << "ms\n";
    return 0;
}

Converting Durations

duration_cast converts between units. Casting from a finer unit to a coarser one truncates, so 1500 ms becomes 1 s.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    milliseconds ms{1500};
    seconds s = duration_cast<seconds>(ms);
    std::cout << s.count() << " whole seconds\n";
    return 0;
}

Arithmetic on Durations

Durations support +, -, *, and /. Mixing units automatically promotes to the finer common unit.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    auto total = minutes{2} + seconds{30};
    std::cout << total.count() << " seconds total\n";
    return 0;
}

Floating-Point Durations

You can use a floating-point representation to keep fractional values when converting, avoiding the truncation of integer durations.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    milliseconds ms{1500};
    duration<double> secs = ms;
    std::cout << secs.count() << " seconds\n";
    return 0;
}

What Is a Clock?

A clock provides the current time. The standard library offers three:

system_clock — wall-clock time
steady_clock — never goes backwards, ideal for timing
high_resolution_clock — finest available tick

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    auto now = steady_clock::now();
    std::cout << "Got a time point: " << (now.time_since_epoch().count() > 0) << '\n';
    return 0;
}

system_clock

system_clock tracks real-world calendar time and can be converted to a time_t for display. It may jump if the system clock is adjusted.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    auto tp = system_clock::now();
    auto secs = duration_cast<seconds>(tp.time_since_epoch());
    std::cout << "Seconds since epoch is positive: " << (secs.count() > 0) << '\n';
    return 0;
}

steady_clock

steady_clock is monotonic: it only moves forward at a constant rate. Use it whenever you measure elapsed time, never system_clock.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    auto a = steady_clock::now();
    auto b = steady_clock::now();
    std::cout << "Monotonic: " << std::boolalpha << (b >= a) << '\n';
    return 0;
}

Clock Resolution

Each clock exposes its period as a compile-time ratio. You can inspect whether a clock is steady at compile time too.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    std::cout << "steady_clock is_steady: " << std::boolalpha << steady_clock::is_steady << '\n';
    std::cout << "system_clock is_steady: " << system_clock::is_steady << '\n';
    return 0;
}

Putting It Together

Combine clocks and durations: read two time points and compute the difference as a duration in your chosen unit.

#include <iostream>
#include <chrono>

int main() {
    using namespace std::chrono;
    auto start = steady_clock::now();
    long sum = 0;
    for (int i = 0; i < 1000000; ++i) sum += i;
    auto end = steady_clock::now();
    auto us = duration_cast<microseconds>(end - start);
    std::cout << "Loop took at least 0 us: " << (us.count() >= 0) << '\n';
    return 0;
}

Quick Check

Test your understanding of which clock to use for timing.

Answer it in the interactive lesson

Recap

You learned that <chrono> provides:

durations — type-safe spans of time with literals like 5s
duration_cast for converting units (truncates integers)
clocks — system_clock, steady_clock, high_resolution_clock
use steady_clock for measuring intervals

Next, you will represent specific moments in time with time points.

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Frequently Asked Questions

Is the “Durations and Clocks” lesson free?

Yes — any 3 lessons of the C++ Academy learning path, including “Durations and Clocks”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The C++ Academy course includes 4 lessons in total.

What will I learn in “Durations and Clocks”?

Measure time intervals. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C++ Academy?

No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “Durations and Clocks” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C++ Academy lesson?

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